Today, President Obama tapped the mayor of Charlotte, North Carolina as his new Transportation secretary. The president says Anthony Foxx understands the connection between public investment in transportation projects and economic revival. In a moment, we'll hear more about Foxx's track record in North Carolina.

But first, as NPR's Scott Horsley tells us, this nomination still leaves a couple of vacancies in the president's Cabinet, three months into his second term.

SCOTT HORSLEY, BYLINE: At the White House this afternoon, President Obama said he hopes for quick Senate confirmation of his Transportation nominee. The president has repeatedly pitched public spending on highway and rail projects as a way to get the country moving again. He says Foxx has the experience to help make that happen.

PRESIDENT BARACK OBAMA: We've got a lot of work to do. Our top priority as a nation right now is doing everything we can to grow our economy and create good jobs and rebuild opportunity for the middle class. And one of the best ways we can do that is to put more Americans back to work rebuilding our infrastructure.

HORSLEY: As a Southerner and an African-American, Foxx would bring additional diversity to the president's Cabinet. Obama drew criticisms earlier this year when he named three white men to fill marquee posts as secretaries of State, Defense and Treasury. That became a punchline for Conan O'Brien at this weekend's White House Correspondents' Dinner.

CONAN O'BRIEN: Seriously, Mr. President, your hair is so white, it could be a member of your Cabinet.

AUDIENCE: Oh.

O'BRIEN: He can handle it.

HORSLEY: Obama has since nominated women as secretary of the Interior, budget director, and EPA administrator, and he's tapped a Latino to serve as secretary of Labor. White House spokesman Jay Carney said today Obama believes diversity in his Cabinet is important to good decision-making.

Presidential scholar Shirley Anne Warshaw of Gettysburg College says, it's a balancing act for any president.

SHIRLEY ANNE WASHAW: The Cabinet, as Bill Clinton said, has to look like America. But to look like America, you don't want to go too far out of your comfort zone. You need people that you trust. You don't have to know them that well, but people that you trust.

HORSLEY: Obama spoke warmly today about his friendship with outgoing Transportation Secretary Ray LaHood, a Republican congressman from the president's home state of Illinois. He praised LaHood for overseeing major road and rail repairs, and for his public campaign against distracted driving.

When LaHood's turn to speak came, he joked that White House staffers had allowed him all of one minute to say goodbye. The former congressman actually spoke for about seven minutes. But Warshaw says Cabinet members have been largely muzzled during the Obama administration because so much domestic policy is set by the White House itself.

WASHAW: This Cabinet, more than any Cabinet in many, many administrations, has not handled the public role that other Cabinets have, particularly to deflect issues away from the president. About the only time you see them talking publicly is when they're speaking before a congressional committee.

HORSLEY: That could be demoralizing for some Cabinet secretaries. But nonetheless, Warshaw says Obama's Cabinet has been unusually loyal. In jobs where the average tenure is just over two years, nearly all of Obama's Cabinet stayed for the whole first term.

About half the Cabinet opted to leave when that term ended, including high-profile figures Hillary Clinton and Tim Geithner. Other secretaries, though, have stayed on, including Attorney General Eric Holder and Health Secretary Kathleen Sebelius.

Today's nomination still leaves two vacancies in the president's Cabinet. Hyatt Hotel heiress Penny Pritzker is expected to get the nod as Commerce Secretary, and economic adviser Michael Froman reportedly will be named U.S. Trade Representative. Those nominations could come as early as this week.